Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $38.97   4.796%   $40.839   $40.84   $40.85   $40.80  
  Purchase #2 $76.48   13.659%   $86.9264   $86.93   $86.95   $86.90  
  Purchase #3 $123.27   6.359%   $131.1087   $131.11   $131.10   $131.10  
  Purchase #4 $189.51   4.211%   $197.4903   $197.49   $197.50   $197.50  
  Purchase #5 $188.62   6.793%   $201.433   $201.43   $201.45   $201.40  
  Purchase #6 $237.25   13.873%   $270.1637   $270.16   $270.15   $270.20  
  Purchase #7 $154.60   7.577%   $166.314   $166.31   $166.30   $166.30  
  7 purchase totals = $1,008.70       $1,094.2751   $1,094.27   $1,094.30   $1,094.20